Senile dementia of the Alzheimer type (SDAT) is generally acknowledged to be the major cause of dementia, a major health problem in this country and the world. The etiology and pathogenesis of this disorder is poorly understood and effective treatment for this disease is unavailable. Recent attention has focused on study of specific central nervous system (CNS) neurotransmitter circuits in SDAT. Post-mortem studies have provided evidence for destruction of cholinergic and somatostatin-containing neurons in the CNS of patients with SDAT. The purpose of the present study is to utilize specific radioimmunoassays developed in this laboratory to measure the levels of three endogenous peptides, somatostatin, neurotensin and thyrotropin-releasing hormone, in selected brain regions of patients with SDAT and age- and sex-matched controls. The brain samples are provided by the MRC Brain Bank in Cambridge, England and the diagnosis of SDAT is made on both clinical and histological grounds. Such data will provide important information on the involvement of neuropeptides in the pathophysiology of SDAT and may lead to the development of novel therapeutic intervention for this devastating disorder.